The explosion aboard the Deepwater Horizon rig on 20 April killed 11 workers and began a devastating spill which leaked over 4 million barrels of oil into the Gulf of Mexico – the largest spill in American history. The leak took three months, and a huge variety of different attempts (see interactive), to seal before BP finally closed it off on 15 July.

The ruptured oil well is still not permanently sealed, with the company announcing last week it will be two weeks before the leak is closed off for good. The leak was only allowed to occur when the blow-out preventer – the last line of defence against an out of control well – failed to activate after the explosion above the surface.

Our team of experts will be poring over the BP report as soon as it is released, with key sections being reported and analysed here. We'll also have the latest reaction from the global markets and from other companies potentially implicated in the spill.

City analysts Evolution Securities said the investigation could shift culpability towards Transocean – which operated the Deepwater Horizon rig on BP's behalf – and "in particular the integrity of the blowout preventer which should have acted as the ultimate fail safe", Graeme reports.

BP also received good news from Fitch this morning, which raised its credit rating on BP to A, from BBB, with a stable outlook.

Fitch said that it was now more confident that the well was capped permanently.

"The "A" rating also reflects both the improved visibility of potential liability scenarios the company could still face and substantial payments that BP has made to date in building up liquidity to address potential financial payments," Fitch added.

Terry Macalister, our energy editor, says a first glance at the BP report confirms expectations that the company would argue that "multiple failures" by a number of different parties were to blame for the fatal blowout.

The report points the finger at Transocean (the rig operator) and Halliburton (the well contractor) as being as much to blame for the disaster as BP. The oil company always claimed to have been unfairly singled out by US politicians and now claims to have the proof that others should be held to account also.

12.23pm:

Damian Carrington, the Guardian's head of environment, writes:

As well as very clearly seeking to spread the blame, the end of BP's press release notes that its report is based on "information available to the investigating team".

Once again, it turns the focus on its contractors: "Additional relevant information may be forthcoming, for example, when Halliburton's samples of the cement used in the well are released for testing and when the rig's blow-out preventer [owned and operated by Transocean] is fully examined now that it has been recovered from the sea-bed."

12.30pm:

The Guardian's Nick Fletcher is following the reaction in the financial world to the report. Shares in BP, which rose this morning, have risen again, he writes.

The stock market seems to like BP's plan to share out the blame for the Gulf spillage, judging by the initial reaction.

The company's shares - already up 6.75p at 413.55p immediately ahead of the report's release - have made further gains now the findings are out. They currently stand at 414.95p, up 8.15p or 2%.

But the market is in a jittery mood and there is no guarantee that things will stay the same once investors have had time to digest the full report. And it is worth bearing in mind BP's shares were at 650p ahead of the disaster on April 20.

12.37pm:

Below the line, bombed writes: "I'm curious, who hired these other companies to work with BP? Was it BP themselves or some authority overseeing the whole endeavour?"

RealPol has the answer: "BP, through the tender process usually."

Interesting point.

12.42pm:

More from Terry Macalister on BP's efforts to share the blame:

Tony Hayward, the BP chief executive, puts part of the blame directly on to US contractor Halliburton (whose former chief executive was previous US vice president, Dick Cheney) which did the "cementing" of the Macondo well.

"To put it simply, there was a bad cement job," said Hayward in a statement which conflicts with a previously published email from a Halliburton employee on the rig to a colleague saying the job "went well."

BP also takes blame away from itself over the "design" of the well. "It would appear unlikely that the well design contributed to the incident," argues Hayward.

7 - The fire prevention system on the rig failed. "The heating, ventilation and air conditioning system probably transferred a gas-rich mixture into the engine rooms". That's where it probably caught fire and destroyed the rig

8 - Key point - the blowout preventer, the ultimate failsafe failed. The fire on the rig stopped the BOP being operated, while an automated system failed in part because the BOP had flat batteries in one control pod and a faulty solenoid valve in another

1.20pm:

More from Damian Carrington:

BP is likely to have had its legal liability for the Deepwater disaster uppermost in its mind and the executive summary bears that out: of the four and half pages of text, the first page is entirely disclaimers of one sort or another. If BP was shown to have been "grossly negligent" then the financial penalties ramp up vastly.

1.26pm:

Terry Macalister wonders what the report suggests re safety practices across the rest of the oil industry:

What is really shocking about this report is the catalogue of errors - both human and mechanical. They demolish once and for all the oil industry's much quoted mantra that "safety always comes first." It may come first in the board room but it does not down at the wellhead where the real dangers are faced.

It is worth remembering that BP, its rig operator Transocean and the main well contractor Halliburton are the blue chip companies in the wider oil and gas sector. If the shoddy work practices highlighted here are what the best-in-class do, then what is happening in the lower reaches of this industry?

1.39pm:

More financial reaction from Nick Fletcher:

The US market is not open yet for reaction, but Transocean's Swiss quoted shares are down nearly 1.5% following the release of the BP report suggesting the drilling contractor missed danger signs on the Deepwater Horizon rig. Meanwhile BP itself has slipped from its best levels but is still up 1.7% at 413.7p.

1.50pm:

Damian Carrington emails: "Reaction to the BP report is starting to flow, and it's not going to be pretty."

This is from Jim Footner, head of Greenpeace's energy campaign.

"This report is a sorry catalogue of the gaffes and failures behind the Deepwater Horizon disaster. And it's highly likely that a truly independent report would be even more damning for BP.

"Worryingly, they're just weeks away from drilling at similar depths in UK waters. The Government must step in right now and stop this by introducing a moratorium on deep water drilling.

"But the real problem is our addiction to oil, which is pushing companies like BP to put lives and the environment at risk. The age of oil is coming to an end and companies like BP will be left behind unless they begin to adapt now. The time has come to move beyond oil and invest in clean energy."

2.04pm:

Our US environment correspondent, Suzanne Goldenberg, has been speaking to Alfred R Sunsen – owner of New Orleans oyster company P&J, which is now facing ruin after 134 years in business.

Sunsen said he believes the report was "pretty thorough", although points out that BP said it carried out the report with limited access to physical evidence.

The oyster business owner writes:

The report does not address the people, businesses, animals, or natural resources that have been impacted by the disaster and will be dealing with the consequences of their inadequate and slow response to the disaster.

Me as well as my friends in the oyster business in Louisiana are in big trouble and will be for some time to come… Talk is cheap.

When BP shows me a report of how exactly they will deal with those people most impacted by this tragedy, i.e. those in the fisheries related businesses, I'll believe they are not just using their talents in public relations to dispel their liability, but have a plan to help us salvage our businesses and retain our livelihoods and heritage, by paying our bills until we are "made whole" as Mr Hayward and Mr Obama said months ago.

Suzanne has just arrived at the Washington DC hotel where Mark Bly – BP's head of safety and operations – is giving a briefing.

•BP has released the findings of its investigation into the oil spill in the Gulf of Mexico. The company has listed eight different issues which let to the Deepwater disaster, including that a test performed to see if the well was under control was accepted – despite the readings showing the well was not under control.

•The company has, as expected, sought to share the blame for the explosion and spill. In a press release accompanying the report Tony Hayward, BP's outgoing chief executive, said: "To put it simply, there was a bad cement job." It was US contractor Halliburton which cemented of the Macondo well.

•The report also points the finger at Transocean, which operated the Deepwater Horizon oil rig. "The negative pressure test was accepted when it should not have been [see top bullet-point], there were failures in well control procedures and in the blow-out preventer; and the rig's fire and gas system did not prevent ignition," Hayward said.

•Greenpeace has criticised BP, describing the report as a "sorry catalogue of gaffes and failures". Jim Footner, head of the charity's energy campaign, said: "It's highly likely that a truly independent report would be even more damning for BP." He added that the company are "weeks away" from drilling at similar depths in UK waters.

•BP's share price rose after the report was published, with shares up by 2% half an hour after publication. Later this afternoon the share price had fallen slightly but was still up 1.7%, at 413.7p. However this is a long way from the 650p BP's shares were trading at before the disaster on 20 April.

No response from the White House yet to the report, although President Obama's press secretary Robert Gibbs was asked about it in yesterday's press briefing.

Gibbs appears to say that the US government had not seen a copy of the report, which seems strange. Here's the exchange:

Q: BP is going to release its report tomorrow into the causes of the oil spill. Has the White House had an advance look at this? And secondly, given the past relationship between the administration and the company, what level of confidence do you have that this is going to produce a genuine finding into what caused the accident?

Gibbs: Well, look, I'll say this. I know of no one that has seen it here. I've certainly seen emails alluding to the notion that -- and clips alluding to the notion that this is -- this will be released. Obviously I think we'd want a chance to look at the report.

I think an important partner of that investigation, Stephen, ultimately is going to get -- is going to be a look at the blowout preventer itself, which only recently, in the last few days, has been brought to the surface, and will give us a chance to see whether was this a design flaw, was this something that was just a problem that this blowout preventer had to deal with, and a whole host of things.

So we'll certainly look through the report. Obviously -- look through the report and may have some comment about it. But I do not know of anybody who has seen an advance copy.

"It's a pretty terrifying picture for a drilling operation that was supposed to be failsafe," Damian says.

3.15pm:

Terry Macalister has sent me what he says could be the key section in BP's report. The final sentence reiterates BP's main argument – "multiple companies" were involved in the failure.

"The team [investigating the explosion] did not identify any single action or inaction that caused this accident. Rather, a complex and interlinked series of mechanical failures, human judgments, engineering design, operational implementation and team interfaces came together to allow the initiation and escalation of the accident. Multiple companies, work teams and circumstances were involved over time."

3.28pm:

Transocean has accused BP of attempting to "conceal" its own failings in today's report, and says the company "made a series of cost-saving decisions that increased risk" during the drilling.

Transocean owned and operated the Deepwater Horizon rig, and is one of the two companies which BP's report says are also responsible for the explosion.

However the company says it was BP's "fatally flawed well design" which set the stage for the incident. It says cost-cutting by BP contributed to the increasing of risk in the design and construction of the Macondo well.

Transocean also appears to hint that BP is holding up its own report into the Deepwater disaster by failing to release evidence.

"This is a self-serving report that attempts to conceal the critical factor that set the stage for the Macondo incident: BP's fatally flawed well design. In both its design and construction, BP made a series of cost-saving decisions that increased risk – in some cases, severely. Those decisions, made exclusively by BP, included:

• Using a long production string rather than a casing tie back, decreasing the number of barriers to gas flow.• Neglecting to run a cement bond log (CBL) to test the integrity of the cement.• Installing fewer than one third of the recommended number of centralizers, dramatically increasing the risk of cement channelling and gas flow.• Failing to conduct a complete "bottoms up" circulation of the well to insure the quality of the cement seal.• Not running a lockdown sleeve to secure the production string to the well head, eliminating yet another barrier to a blowout.

Transocean's investigation is ongoing, and will be concluded when all of the evidence is in, including the critical information the company has requested of BP but has yet to receive."

Graeme adds that Wall Street is now open, and says Transocean's shares are actually up in early trading, so far gaining 1.5% in New York.

"Cameron International, which made the blowout preventer that failed to stop the leak, are also up nearly 1.7%. Halliburton has taken a hit, though, down around 0.3%," Graeme said.

"BP's own shares are currently up around 1.5% in London. So traders are taking this report in their stride, so far..."

4.09pm:

The publication of BP's report is headline news on many US news websites.

Because of its authorship, the report is unlikely to carry much weight in influencing the Department of Justice, which is considering criminal and civil charges related to the spill.

The report is, however, as much a public relations exercise as a preview of BP's probable legal strategy as it prepares to defend itself against possible federal charges, penalties and hundreds of pending lawsuits.

WWL-TV, a news channel based in Louisiana, one of the states affected by the spill, said BP had "spread the blame around", but pointed out that "in public hearings, it had already tried to shift some of the blame to rig owner Transocean Ltd. and cement contractor Halliburton".

It added:

BP's report is far from the final word on possible causes of the explosion, as several divisions of the U.S. government, including the Justice Department, Coast Guard and Bureau of Ocean Energy Management, Regulation and Enforcement, are also investigating.

4.31pm:

Suzanne Goldenberg has spoken with Wayne Pennington, head of the geological engineering department at Michigan Technical University.

Pennington notes that BP's finger pointing at Halliburton and Transocean still leaves important questions unanswered about the safety decisions it took itself:

While blame for some errors can perhaps be assigned to the contractors working for BP, the blowout and subsequent explosion and spillage appear to the result of an overall attitude that encouraged unwarranted optimism in the quality of each component of the job, allowing the omission of standard testing procedures, and the misinterpretation of other tests in the most-favorable light.

Instead, skepticism should reign on any drilling job, and testing and evaluation at each stage of the drilling and completion would then be routine; instead of questioning the need for such things as the cement bond log, the companies involved should insist on checking and double-checking quality at each step of the process. This was clearly not done, repeatedly, in the case of the Macondo well, and disaster resulted.

OK – bear with me on this one – it's a key bit of finger-pointing between Transocean and BP.

Transocean, the rig operators, say the decision was made "exclusively by BP" to install "fewer than one third of the recommended number of centralizers, dramatically increasing the risk of cement channeling and gas flow". To translate, centralisers keep the bore hole in shape while the cement is poured in, allowing it to form a better seal. Transocean accuse BP of cost-cutting.

BP says in its report that modelling showed that using 21 centralizers could reduce the chances of a leak. The equipment they were using had only six centralizers, so they got another 15 sent to the rig. But "the BP Macondo well team erroneously believed that they had received the wrong centralizers. They decided not to use the 15 centralizers due to a concern that these ... could fail."

So on this key point, BP appears to accept that its team made the mistake.

5.12pm:

A 5pm (or thereabouts) summary:

• BP's report into the Deepwater Horizon explosion lists eight separate findings which contributed to the blast. The company admits some culpability; that some of its staff misinterpreted readings regarding the pressure in the well, and that BP workers only used six centralisers – which keep the well bore hole in shape and reduce the chances of a leak – when BP had intended them to use 21.

• Although it admitted some responsibility, the company has sought to share the blame, mentioning Transocean and Halliburton as also at fault. BP listed a number of failures committed onboard the rig, which was operated by Transocean. Outgoing BP chief exec Tony Hayward also said today: "To put it simply, there was a bad cement job." It was the contractor Halliburton which cemented of the Macondo well.

• Transocean has struck back this afternoon however, accusing BP of trying to conceal its own failings in the report. It says the company "made a series of cost-saving decisions that increased risk" during the design and construction of the well. Transocean also appears to hint that BP is holding up its own report into the Deepwater disaster by failing to release evidence.

• The financial world has so far reacted positively to the report, with BP shares in London up 1.3% at closing. Share price closed at 412.15p, up 5.35p on the day. In the US Cameron International and Transocean are currently around 2% higher than opening while even Halliburton – down initially – has recovered to show a 1.5% increase.

That's all from me in London, but stay tuned, my colleague Richard Adams will shortly be taking over to cover the rest of the day's developments from the US.

5.30pm: Good afternoon, this is Richard Adams in the Guardian's Washington DC bureau, taking over from Adam's excellent work.

The US media is still getting its collective head around the BP report but reaction is starting to trickle out, although so far it's mainly just straight news coverage of the report.

If nothing else this will be more grist for the Onion, along the lines of: "BP report clears BP of BP oil rig disaster". Except that wouldn't be satire.

Throughout the Gulf oil spill, BP's high-ranking officials have touted what they call the firm's culture of safety and responsibility. But that self-proclaimed culture of safety is not what's reflected in the shortcuts BP engineers took on the Deepwater Horizon rig, ignoring warnings and leading to the death of 11 workers and the worst oil spill in the nation's history.

5.50pm: My hard-working colleague Damian Carrington is polishing off a blockbuster analysis of where BP is putting the blame, which will appear on the Guardian's site soon – I'll link to the article as soon as it's up.

But in the meantime, here's a sneak preview from Damian:

The eight big things that went wrong are, engineers tell me, a logical and plausible explanation. But who's fault were they, according to BP? My explanations are below, but to cut to the chase, the BP report appears to pin 4.5 of the 8 problems on Transocean, 1 on Halliburton and 1.5 on BP, with one undecided.

More to come on this.

6.10pm: Of course, some people – cynics mainly, hippies and so on – aren't convinced by BP's own report (although if you can't believe a giant, profit-seeking multinational corporation, who can you believe?). Those sort of people would probably prefer to get their information from an independent source. In that case you really should read this sterling and lengthy analysis published in the Times-Picayune:

BP's Gulf drilling manager, David Sims, acknowledged in testimony that "every conversation, every decision has a cost factor." E-mail messages and reports by BP engineers in the weeks before the accident make reference to money or time savings as they debated methods for closing the well. In each case, they went the cheaper way.

Fancy that.

6.39pm: Insightful commentary from Geoffrey Maitland, professor of energy engineering at Imperial College in London and an expert in the field. He says the report gave an analysis of the disaster that would not surprise anyone in the oil industry – but "it tries to put the best light on it for BP, as you'd expect for an internal report which will play a part in legal actions in the future."

"What is not there is interesting. BP says the well design was not a factor. Transocean say it is and I think Halliburton think the same."

Prof Maitland notes that a preliminary report by the US Congress back in June raised six points about well design but that very few of those are addressed in BP's report:

"The BP report gives lots of detail but it does not give the detail needed on how the decisions were taken in the critical areas and how the decision making was shared."

"You will get the lawyers playing some very clever games about which path to take through the maze of cause and effect, depending on who their client is."

7pm: Halliburton has finally put out an official response to BP's report – and the signs are that it is going to come out swinging.

This is from Cathy Mann, director of corporate affairs at Halliburton:

As we continue to review BP's internal report published earlier today, we have noticed a number of substantial omissions and inaccuracies in the document.

Halliburton remains confident that all the work it performed with respect to the Macondo well was completed in accordance with BP's specifications for its well construction plan and instructions, and that it is fully indemnified under its contract for any of the allegations contained in the report.

Deepwater operations are inherently complex and a number of contractors are involved which routinely make recommendations to a single point of contact, the well owner. The well owner is responsible for designing the well program and any testing related to the well. Contractors do not specify well design or make decisions regarding testing procedures as that responsibility lies with the well owner.

I'll stick my neck out here and say that sounds like a longer version of "We'll see you in court".

The report says: "The BOP maintenance records were not accurately reported in the maintenance management system. The condition of critical components in the yellow and blue [control] pods and the use of a non-[original] part, which were discovered after the pods were recovered, suggest the lack of a robust Transocean maintenance management system." BP's verdict: Transocean to blame

Strangely enough, Transocean are to blame for five of the eight big problem areas, according to BP. But of course, it was BP that hired Transocean....

8pm: The FT's Lex columnists think the report was a generally good thing for BP to have done, on the grounds that: "At least BP has spoken first. It can now get ahead of its peers in improving rig safety." That would be BP's peers who haven't had a giant oil spill disaster.

The FT has been reliably pro-BP throughout the entire Gulf spill, and that hasn't changed based on today's Lex note (which may be behind a paywall):

BP has never sought to dodge its responsibilities; hence the prompt decision to write an unlimited clean-up cheque – $8bn so far. Still, the company would like to avoid falling into the expensive legal hell that would come with the finding of "gross negilgence". The report, in essence, is a defence against that charge. It presents a credible narrative that suggests an unfortunate concatenation of errors, each more serious than the last, from many actors, rather than one single big mistake.

The narrative may be credible, but is the source?

8.27pm: The industry reaction in the US appears to pick out BP's focus on the cement used in the well as a significant cause of the blow-out.

FuelFix, the energy blog at the Houston Chronicle formerly known as NewsWatch Energy, has a sharp take:

The BP investigators stressed eight problems and failures that may have culminated with the April 20 rig explosion that left 11 workers dead and triggered the nation's worst offshore oil spill. But they repeatedly honed in on the failure of the cement job at the site, a focus that shifts attention to the work done by the cement contractor Halliburton.

So, it was the cement wot done it? Not quite: "Ultimately, though, the team said that a bad cement job, in and of itself, shouldn't have caused the lethal escape of natural gas from the well."

8.52pm: One of BP's most vocal and influential critics, Congressman Ed Markey, who chairs the House of Representatives's energy and environment subcommittee, is also not impressed by BP's effort:

"This report is not BP's mea culpa. Of their own eight key findings, they only explicitly take responsibility for half of one. BP is happy to slice up blame, as long as they get the smallest piece."

Markey says he's still waiting to hear "the real story of this disaster" from the various independent inquiries taking place.

9.18pm: There has been a reaction from the White House, although a rather low-key one. The White House press secretary Robert Gibbs told reporters that the administration was reviewing BP's report but would continue with its own investigations:

"Our job is to find out what went wrong and hold those responsible ... for the damage that's been done, and that's what the administration will do."

9.45pm: The aftershocks of the BP spill continue to be felt in Washington, especially at the government agency formerly known as the Minerals Management Service, which has suffered from staffing shortages and a cozy relationship with the oil industry.

This afternoon the Obama administration announced it will spend $29m on training offshore drilling inspectors and upgrading enforcement this year, and another $100m next year. The agency hopes to hire hundreds of new inspectors to supplement the 60 responsible for overseeing 3,500 rigs and platforms in the Gulf of Mexico.

10pm: One question is, what other inquiries are there into the Gulf oil spill and Deepwater Horizon disaster? There are about 11 others, believe it or not, but there are three that really count.

Here's a rundown of the big three:

• The Department of Justice and Environmental Protection Agency's criminal investigation. This is the most important and the one that is most likely to lead to prosecutions and steep fines, assuming it's not settled beforehand.

• The joint US Coast Guard-Bureau of Ocean Energy Management investigation. This is the federal investigation that has made the most progress and will be most influential within the government.

• The Chemical Safety and Hazard Investigation Board. BP has 'previous' in front of the CSB, which extensively investigated BP's 2005 Texas City refinery explosion. High on credibility but low on its ability to punish the wrongdoers here, and could take two years to complete.

10.16pm: The Houston Chronicle probably has stronger coverage of the US oil industry than any other US media outlet, because of the high concentration of the industry in the city. But it doesn't pull any punches. Here's business columnist Loren Steffy on the BP report. He says it's deja vu all over again:

Today's Bly report follows a template established by the Mogford Report, issued a few months after the March 2005 explosion at BP's Texas City refinery that killed 15 people. That report, too, placed blame far down the management chain, laying it at the feet of contract workers and mid-level managers.

The article is tastefully illustrated with Britney Spears' Oops!... I Did It Again artwork.

One observer familiar with the BP report, who asked not to be named because he is a member of a federal investigative commission, faulted it for not responding to key questions: "Who was in charge at each step – which employer and position, not which individual – was involved in and responsible for making decisions about what specific equipment, materials, and especially procedures?" the observer said in an e-mail. "What information would be provided to help or be a reference for the rig site personnel in implementing those decisions?"

Among the report's most significant conclusions, investigators say that the blowout came up the center of the pipe and not up the outside of the well casing, the area known as the annulus.

If true, the finding is significant because it plays down the importance of certain BP decisions that have been criticized as negligent. One such decision was BP's choice of a type of well casing that internal documents indicated the company knew was cheaper but riskier. Another such decision was BP's use of fewer-than-advised centralizers, devices that are meant to keep the casing properly positioned.

The report offers scant insight into why certain decisions were made and by whom – questions that are likely to become important in coming legal battles.

For example, the report does not say why the crew failed to notice that the well was flowing until it was too late. It does not clearly explain why the blowout preventer shear rams failed to seal the well when they were eventually closed after the explosion.

11.39pm: Time to wrap things up for the night, since the latest commentary is either reheating the same points – the report is all about BP's looming legal defence – or starting to get so wonky that you need a PhD in engineering to understand the discussion about flapper valves, annuluses (annuli?), shear rams and float collars. (Come to think of it, that sounds more like a nasty Craigslist personals ad.)

Within BP the report might even be counted as a qualified success: some not-bad PR, some legal cover and, as AP reports, even a bump up in its share price:

Energy stocks rose after Fitch Ratings raised its credit rating of BP. BP also released an internal report that largely spread blame from the oil spill in the Gulf of Mexico to rig owner Transocean and contractor Halliburton as well as itself.

The curious effect of all this blame-shifting is that it provides the reader with a rare peek into the workings of the offshore-drilling industry – and a very ugly sight it is too.... BP and the companies working for it are among the best in the business: just imagine how the cowboy outfits behave.